Method and apparatus for providing seamless call handoff between networks that use dissimilar transmission methods

ABSTRACT

Call handoff from an 802.1x network to a cellular network, and vice versa. A wireless device that has both cellular and 802.1x capability detects the strength of a cellular signal and of an 802.1x signal. If a call is taking place over the 802.1x network and the strength of the 802.1x signal drops below a particular level and the strength of the cellular signal is above a certain level, the call is handed off from the 802.1x network to the cellular network. If a call is taking place over the cellular network and the cellular signal strength drops below a certain level while the 802.1x signal strength is above a certain level, the call is handed off from the cellular network to the 802.1x network. In addition, the user of the wireless device can manually initiate the handoff by actuating a handoff selector of the wireless device.

This application is a continuation of U.S. patent application Ser. No.10/742,153, filed Dec. 19, 2003, now U.S. Pat. No. 7,801,529, thecontent of which is hereby incorporated by reference herein in itsentirety into this disclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications and, moreparticularly, to seamlessly handing off a call from one wireless networkthat uses a particular transmission method to a different wirelessnetwork that uses a different transmission method.

2. Description of Related Art

Devices are available that have both cellular capability and capabilityto perform under the standard of the Institute of Electrical andElectronics Engineering (IEEE) known as the IEEE 802.1x standard. Suchdevices include, for example, laptop computers and personal digitalassistants (PDAs). Cellular networks use transmission methods that aredifferent from the transmission methods used in 802.1x networks. Thetransmission methods used by cellular networks are governed by standardssuch as WCDMA, GPRS, 1XRT, 3XRT and EDGE, for example. The transmissionmethods used by 802.1x networks are governed by the applicable IEEE802.1x standard. The term 802.1x, as that term is used herein, means allof the IEEE standards that have the prefix 802.1, including, but notlimited to, 802.11, 802.11a, 802.11b, 802.11c, 802.11d, 802.11e,802.11f, 802.11g, 802.11h, 802.11i, etc. 802.1x networks use theTransport Control Protocol/Internet Protocol (TCP/IP) to enable wirelessdevices with 802.1x capabilities to wirelessly connect to access pointsof wired and wireless local area networks (LANs). Voice, data, video andaudio are transmitted over 802.1x networks in TCP/IP packets.

An 802.1x network access point has a limited distance over which it cancommunicate with a wireless device. When the 802.1x device moves out ofrange of the access point, the call is dropped. The call may becommunicating voice, data, video or audio at the time it is dropped.There may be times when an 802.1x-capable device, such as a PDA, forexample, is out of range of a 802.1x access point, but within range of acellular base station transmitter. However, even though devices existthat have both cellular and 802.1x capabilities, such devices do nothave the capability to seamlessly switch from communicating over an802.1x network to communicating over a cellular network, or vice versa.Therefore, the user is faced with having to manually establishcommunication with the cellular network after the call has been dropped.Of course, resuming a call in this manner may result in informationbeing lost, regardless of whether voice, data, video or audio is beingcommunicated. An analogous situation occurs when a device moves out ofrange of a cellular network and within range of an access point of an802.1x network.

It would be desirable to provide the capability of performing a seamlesshandoff of a call from an 802.1x network to a cellular network, and viceversa.

SUMMARY OF THE INVENTION

The present invention provides for seamless call handoff from an 802.1xnetwork to a cellular network. The wireless device of the presentinvention has both cellular and 802.1x capability. In order for handoffsto occur automatically and seamlessly, signal strength detectioncircuitry in the wireless device detects the strength of a cellularsignal being transmitted by a cellular network and of an 802.1x signalbeing transmitted from an access point of an 802.1x network. If a callis taking place over the 802.1x network and the strength of the 802.1xnetwork signal drops below a particular level while the strength of thecellular signal is above a certain level, the call is handed off fromthe 802.1x network to the cellular network. The wireless devicepreferably also comprises a handoff selector that allows the user tomanually initiate a handoff and to manually override a handoff.

In accordance with the preferred embodiment, not only is it possible toperform a seamless handoff from an 802.1x network to a cellular network,but also from a cellular network to an 802.1x network. In accordancewith the preferred embodiment, seamless handoffs occur in bothdirections. If a call is taking place over the cellular network and thecellular signal strength drops below a certain level while the 802.1xsignal strength is above a certain level, the call is handed off fromthe cellular network to the 802.1x network. If a call is taking placeover the 802.1x network and the strength of the 802.1x network signaldrops below a particular level while the strength of the cellular signalis above a certain level, the call is handed off from the 802.1x networkto the cellular network.

In accordance with the preferred embodiment, when a call is to be handedoff from the 802.1x network to the cellular network (i.e., when thestrength of the signal from available access points has dropped below acertain level), the wireless device queries the cellular network forsignaling and IP connectivity information. When the wireless devicereceives this information, the wireless device communicates it to theSIP or equivalent server of the 802.1x service providing network. Theserver communicates with the media gateway to set up the new connectionbetween the terminating station and the wireless device over thecellular network connection. When communication between the mediagateway and the cellular carrier is given preference, the call on the802.1x network may be terminated. This termination occurs after the“voice” path has been established and determined to be stable.

When a call is to be handed off from the cellular network to the 802.1xnetwork, the wireless device queries the 802.1x network for signalingand IP connectivity information. When the wireless device receives thisinformation, the wireless device communicates it to the call controlserver (e.g., an SIP or equivalent server) of the service providingnetwork. The call control server communicates with the media gateway toset up the call on the 802.1x network with the new connection betweenthe terminating station and the wireless device over the 802.1x network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the connectivity between a wirelessdevice and an 802.1x network when a call is established between thewireless device and a terminating station that is connected to the802.1x network via a Plain Old Telephone Service (POTS) network, alsocommonly known as Public Switched Telephone Network (PSTN), and a mediagateway.

FIG. 2 is a block diagram showing the connectivity between a wirelessdevice and a cellular network when a call that was initially establishedover the 802.1x network is handed off to the cellular network tomaintain a connection between a wireless device and the terminatingstation that is connected to the cellular network via a POTS network anda media gateway.

FIGS. 3A and 3B together illustrate a flow chart of the method of thepresent invention in accordance with a preferred embodiment forseamlessly handing off a wireless device call from an 802.1x network toa cellular network.

FIGS. 4A and 4B together illustrate a flow chart of the method of thepresent invention in accordance with a preferred embodiment forseamlessly handing off a wireless device call from a cellular network toan 802.1x network.

FIG. 5 is a block diagram of a media gateway connected to a cellularnetwork and to an 802.1x network.

FIG. 6 is a flow chart illustrating an embodiment of the methodperformed by the call control server shown in FIG. 2 to cause a callhandoff from an 802.1x network to a cellular network to occur, and viceversa.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a diagram of an 802.1x network that illustrates connectionsmade over the 802.1x network when a call from a wireless device 1 isbeing serviced by the 802.1x network 2. In the example shown, thewireless device 1 is a PDA that initiates a call to a terminatingstation 3 of a plain old telephone service (POTS) network 4. Thewireless device 1 could be any type of wireless device. A media gateway5 provides the necessary connectivity between the 802.1x network 2 andthe POTS network 4. The terminating station 3 is shown as being atelephone in this example, although it could be any type of terminatingdevice. Also, although the call is shown in this example as terminatingat a POTS terminating station 3, the call could instead terminate at awireless device (not shown) in communication with a cellular network,such as cellular network 6, for example, having cellular switching withInternet Protocol (IP) connectivity.

The media gateway 5 also interfaces the cellular network 6 with the802.1x network 2. It should also be noted that the call could beinitiated by a wireless device communicating over the cellular network6, in which case the media gateway would route the call over the 802.1xnetwork 2 to the wireless device 1. Similarly, the call could beinitiated by the terminating station 3 and directed to the wirelessdevice 1, in which case the media gateway 5 would route the call fromthe POTS network 4 to the wireless device over the 802.1x network 2. Thepresent invention is equally applicable to each of these scenarios, asdescribed below in more detail.

In accordance with the present invention, the wireless device 1 has bothcellular and 802.1x capabilities. The wireless device 1 also hasintelligence that enables it to sense the strength of the signal betweenthe wireless device 1 and the access point 7 of the 802.1x network 2 andthe strength of the signal between the wireless device 1 and thecellular network 6. In accordance with the preferred embodiment, whenthe wireless device 1 is communicating over the 802.1x network 2 (i.e.,the 802.1x network 2 is servicing the call), it is also querying thecellular network 6 so that it can measure the strength of the responseto the query from the cellular network 6. Simultaneously, while thewireless device 1 is communicating with the access point 7, it is alsomeasuring the strength of the signal received from the access point 7.When the strength of the signal received from the access point 7 dropsbelow a certain level and the strength of the signal received fromcellular network 6 is above a certain level, the call is handed off fromthe 802.1x network 2 to the cellular network 6. Once the call is beingserviced by the cellular network 6, the connection between the wirelessdevice 1 and the 802.1x network 2 preferably is severed.

Similarly, when the wireless device 1 is communicating over the cellularnetwork 6 (i.e., the cellular network 6 is servicing the call), it isalso querying the 802.1x network 2 so that it can measure the signalstrength of the response to the query from the access point 7.Simultaneously, while the wireless device 1 is communicating with thecellular network 6, it is also measuring the strength of the signalreceived from the cellular network 6. When the strength of the signalreceived from the cellular network 6 drops below a certain level and thestrength of the signal received from access point 7 is above a certainlevel, the call is handed off from the cellular network 6 to the 802.1xnetwork 2. Once the call is being serviced by the 802.1x network 2, theconnection with the cellular network 6 preferably is severed. The term“severed”, as that term is used herein, means that the resources thatwere being used to handle the call prior to the handoff are released.

Because the call is not severed until the new connection is established,no information is lost and there is no discontinuity with the call,regardless of whether voice, data, video or audio is being transmitted.A call control (e.g., session initiation protocol (SIP)) server 10 ofthe network 2 handles call signaling, call routing, capabilitiesexchange, media control and supplementary services. As an alternative toa SIP server, an equivalent type of server could be used, such as, forexample, an H.323 server. When the wireless device 1 initiates a call tothe 802.1x network 2, the access point 7 communicates information to theserver 10 that the server 10 records, including the IP address of thewireless device 1, the “IP” address of the terminating station 3, theconnect time of the wireless device 1 and the ID of the wireless device1. The connect time is recorded for billing purposes and the IP addressof the wireless device 1 that originates the call, the “IP” address ofthe terminating station 3 and the ID of the wireless device 1 are neededfor call signaling and call routing. The server 10 then communicatesinformation to the media gateway 5 that allows the media gateway 5 tomake the connection between the IP address of the wireless device 1 andthe IP address of the local exchange switch 11 that corresponds to theterminating station 3.

At the local exchange switch 11, the IP address associated with theterminating station 3 is converted into a physical POTS address and aphysical connection is made between the terminating station 3 and thelocal exchange switch 11. The media gateway 5 comprises intelligence forconverting the signals from the TCP/IP addressing format into signalsconditioned for the POTS network 4, and vice versa.

FIG. 2 is identical to FIG. 1 except that it shows a connection 15between the cellular network 6 and the media gateway 5 to represent thewireless device 1 communicating with the terminating station 3 when themedia gateway 5 receives the IP connectivity information sent from thecellular network 6 and transmitted by the wireless device 1 to theaccess point 7 and makes the new connection. The wireless device 1preferably consistently take samples of ambient signals available in thespectrum (i.e., the access point transmissions). When the wirelessdevice 1 determines that the strength of the signal received from theaccess point 7 has dropped below a certain level and that the strengthof the signal received from the cellular network 6 is at or above acertain level, the wireless device 1 queries the cellular network 6 toobtain the signaling and IP connectivity information needed for thehandoff from the 802.1x network 1 to the cellular network 6. Thewireless device 1 will first recognize an available signaling network,and then attempt to access data service (e.g., GPRS, EDGE, 1XRT, etc.).If these fail, another network will be interrogated. This does notwidely vary from current cellular attachment to data networks.

The wireless device 1 communicates the signaling and IP connectivityinformation to the access point 7, which communicates the information tothe SIP or equivalent (e.g., H.323) call control server 10. The server10 records this information, which includes the IP address that thecellular network 6 has assigned to the wireless device 1 for it to usein the handoff. The server 10 changes the IP address of the wirelessdevice 1 from the one that was recorded when the call was initiated tothe new IP address assigned by the cellular network 6. The server 10then provides the media gateway 5 with the new IP address of thewireless device 1 on the cellular network 6, thereby causing the newcommunication link between the wireless device 1 connected to thecellular network 6 and the terminating station 3 connected to the POTSnetwork 4 to be established. Once the new connection is established, theserver 10 causes the access point 7 to severe its wireless connectionwith the wireless device 2. Alternatively, the wireless device 1, ratherthan the server 10, will terminate the 802.1x connection and release theresources. Because, the original connection is not severed until afterthe new connection has been established, the handoff is seamless. Theline 15 from the cellular network 6 to the media gateway 5 representsthe new connection.

FIGS. 3A and 3B illustrate a flow chart of the method of the presentinvention in accordance with the preferred embodiment for performing aseamless handoff from the 802.1x network 2 to the cellular network 6.The call is initiated by the wireless device 1 and established betweenthe wireless device 1 and the terminating station 3, as indicated byblock 21. While the call is being service by the 802.1x network 2, thestrengths of the signals from the access point 7 and from the cellularnetwork 6 are detected by the wireless device 1, as indicated by block22. A determination is made as to whether the strength of the signalfrom the access point 7 has dropped below a certain threshold level, asindicated by decision block 23. If so, a determination is made as towhether the strength of the signal from the cellular network is at orabove a certain threshold level, as indicated by decision block 24. Ifthe answer to either of these questions is no, the process returns toblock 22. The order in which steps 23 and 24 are performed can bereversed.

If the answer to both of the questions of blocks 22 and 23 is yes, thenthe wireless device 1 queries the cellular network 6 for signal and IPconnectivity information, as indicated by block 25. The wireless device1 receives the signal and IP connectivity information from the cellularnetwork 6 and communicates it to the access point 7, as indicated byblock 26. The access point 7 communicates the information, whichincludes the new IP address that will be used for the wireless device 1,to the SIP server 10, as indicated by block 27 in FIG. 3B. The SIPserver 10 then records the new IP address of the wireless device 1 andcauses the media gateway 5 to establish the new connection, as indicatedby block 28. The access point 7 then severs the connection with thewireless device 2, as indicated by block 29. The step represented byblock 29 is optional, but preferred.

FIGS. 4A and 4B illustrate a flow chart of the method of the presentinvention in accordance with the preferred embodiment for performing aseamless handoff from the cellular network 6 to the 802.1x network 2.The method is very similar to the method for performing the handoff fromthe 802.1x network 2 to the cellular network 6. The call is initiated bythe wireless device 1 on the cellular network 6 and established betweenthe wireless device 1 and the terminating station 3 via the mediagateway 5 and the LEC switch 11, as indicated by block 41. While thecall is in progress, the strength of the signals from the access point 7and from the cellular network 6 is measured by the wireless device, asindicated by block 42. A determination is made as to whether thestrength of the signal from the cellular network 6 has dropped below acertain threshold level, as indicated by decision block 43. If so, adetermination is made as to whether the strength of the signal from the802.1x network 2 is at or above a certain threshold level, as indicatedby decision block 44. If the answer to either of these questions is no,the process returns to block 42. As with blocks 23 and 24, the stepsrepresented by blocks 43 and 44 can be reversed.

If the answer to both of these questions is yes, then the wirelessdevice 1 queries the access point 6 for signal and IP connectivityinformation, as indicated by block 45. The wireless device 1 receivesthe signal and IP connectivity information from the access point 7 andcommunicates it to the cellular network 6, as indicated by block 46. Thecellular network 6 communicates the new IP address of the wirelessdevice 1 to the media gateway 5, which establishes the new IP connectionfor the wireless device 1 on the 802.1x network 2, as indicated by block47. The connection between the cellular network 6 and the wirelessdevice 1 preferably is then severed, as indicated by block 48.

As stated above, the wireless device 1 preferably also comprises ahandoff selector switch that allows the user to initiate the handoff andto override a handoff. In some cases, the detected strength levels ofthe signals from both the cellular network 6 and the 802.1x network 2may be sufficiently high to enable the call to be handled by eithernetwork. The user may desire, for one or more of a variety of reasons(e.g., technology, speed, convenience, money, etc.), to switch fromcommunicating over one of these networks to communicating over theother. To accomplish this, the user actuates the handoff selectorswitch, which causes the operations represented by blocks 25-29 or 45-48in FIGS. 3A-4B to occur. The selector switch may be any type of inputdevice that enables a user to make a selection. For example, theselection could be made by depressing a key on a keypad, by highlightingand selecting an item in a menu, etc.

The selector switch may also be used to override an impending handoff.For example, if an automatic handoff from the 802.1x network 2 to thecellular network 6 is impending due to the fact that the thresholdconditions in blocks 23 and 24 of FIG. 3A have been met, the handoffwill be prevented if the selector switch has been activated. This isuseful where the user wishes to continue communicating over the 802.1xnetwork 2 rather than switch to communicating over the cellular network6.

FIG. 5 is a block diagram of the media gateway 5 shown in FIG. 1. Theswitching logic in the media gateway 5 that enables the call session tobe switched from the 802.1x network 2 to the cellular network 6, andvice versa, is represented by the box labeled 50. The gateway 5 is shownas being interfaced with the call control server 10 and with the LECswitch 11 shown in FIG. 1. As indicated above, the call control server10 is part of the 802.1x network 2 and the LEC switch 11 is part of thePOTS network 4. The cellular network 6 interfaces to the gateway 5 via aserving GPRS support node (SGSN) 51, which provides the IP interfacebetween the cellular network 6 and the gateway 5. The dashed arrows 52and 53 in block 50 represent the connections in the gateway 5 that areswitched when a handoff occurs. When a call is handed off from the802.1x network 2 to the cellular network 6, connection 53 is made andconnection 52 is eliminated. When a call is handed off from the cellularnetwork 6 to the 802.1x network 2, connection 52 is made and connection53 is eliminated. FIG. 6 is a flow chart illustrating an embodiment ofthe method performed by the call control server 10 in conjunction withthe media gateway 5 to enable handoffs to occur.

The server 10 determines whether or not a call session is active, asindicated by block 61. Until a session is active, a handoff cannotoccur. Once a determination is made that a session is active, theprocess proceeds to block 62 and the server 10 retrieves both thecellular and 802.1x signal levels. A determination is then made at block63 as to whether the 802.1x signal level is exceeds the cellular levelplus an amount “X”. The value of X can be 0 or any other value, positiveor negative. When a determination is made at block 63 that the 802.1xsignal level exceeds the cellular level plus X, the call control server10 causes the media gateway 5 to switch the call from connection 53 toconnection 52 unless connection 52 already exists, as indicated by block64. If connection 52 already exists, no handoff needs to occur, and soconnection 52 will continue to be maintained. If connection 52 does notyet exist because the call is currently being handled by the cellularnetwork, connection 52 will be made and connection 53 will be eliminatedto free up the resources that were being used for the call over thecellular network.

If a determination is made at block 63 that the 802.1x signal level doesnot exceed the cellular signal level plus X, the call control server 10causes the media gateway 5 to switch the call from connection 52 toconnection 53 unless connection 53 already exists, as indicated by block65. If connection 53 already exists because the call is currently beinghandled by the cellular network, no handoff needs to occur. In thatcase, connection 53 will continue to be maintained. If connection 53does not yet exist because the call is currently being handled by the802.1x network, connection 53 will be made and connection 52 will beeliminated to free resources that were being used to service the callover the 802.1x network.

In an embodiment, the value of X can be altered manually by activatingthe aforementioned selector switch. For example, activation of theselector switch could cause the value of X to increase to prevent thecondition in block 63 from being true, which would prevent a handofffrom the cellular network to the 802.1x network from occurring. If thecellular network is currently handling the call, the cellular networkwill continue to handle the call. Alternatively, actuation of theselector switch could cause the value of X to decrease or becomenegative, thereby ensuring that the condition of block 63 is true. Thiswould ensure that a handoff from the cellular network to the 802.1xnetwork occurs or, if the call is currently being handled by the 802.1xnetwork, the connection with the 802.1x network would continue to bemaintained. As another alternative, the selector switch could havemultiple states so that selection of one sate would cause the value of Xto increase whereas selection of another state would cause the value ofX to decrease. Alternatively, multiple selector switches could beprovided. It should be noted that the method shown in FIG. 6 is only oneof a variety of methods that could be used to accomplish the objectivesof determining when a handoff is to occur, handing the call off when adetermination has been made that a handoff should occur, and/oroverriding the handoff.

It should be noted that although the present invention has beendescribed with reference to particular embodiments, the presentinvention is not limited to the embodiments described herein.Modifications can be made to the embodiments described herein and allsuch modifications are within the scope of the invention.

1. A system for switching a call session, the system comprising: an802.1x network; a cellular network; a media gateway in communicationwith the 802.1x network and the cellular network; a wireless deviceconnected to the 802.1x network by a first connection, the 802.1xnetwork connecting the wireless device to a terminating station throughthe media gateway to create a call session, the wireless devicemeasuring a first signal strength of the 802.1x network and a secondsignal strength of the cellular network; and a call control server, thecall control server receiving the first signal strength and the secondsignal strength, the call control server containing logic to determinewhether the second signal strength exceeds the first signal strength byan amount, wherein if the second signal strength exceeds the firstsignal strength by the amount the call control server causes the mediagateway to switch the wireless device from the first connection to asecond connection to the cellular network, and if the second signalstrength does not exceed the first signal strength by the amount thewireless device remains connected through the first connection, whereinthe amount may be adjusted at the wireless device by increasing ordecreasing the amount.
 2. The system of claim 1, wherein the amount isadjusted manually using a selector switch onboard the wireless device,the selector switch having multiple states to manually increase ordecrease the amount.
 3. The system of claim 1, further comprising aserving GPRS support node (SGSN) connecting the cellular network to themedia gateway.
 4. The system of claim 1, further comprising an accesspoint connecting the
 802. 1x network to the media server.
 5. The systemof claim 1, further comprising a local exchange carrier (LEC) switchconnecting the media gateway to a plain old telephone service (POTS)network.
 6. The system of claim 5, wherein the terminating station is onthe POTS network.
 7. A system for switching a call session, the systemcomprising: a cellular network; an 802.1x network; a media gateway incommunication with the 802.1x network and the cellular network; awireless device connected to the cellular network by a first connection,the cellular network connecting the wireless device to a terminatingstation through the media gateway to create a call session, the wirelessdevice measuring a first signal strength of the cellular network and asecond signal strength of the 802.1x network; and a call control server,the call control server containing logic to determine whether the callsession is active, the call control server receiving the first signalstrength and the second signal strength and the logic determiningwhether the second signal strength exceeds the first signal strength byan amount, wherein if the second signal strength exceeds the firstsignal strength by the amount the call control server causes the mediagateway to switch the wireless device from the first connection to asecond connection to the 802.1x network, and if the second signalstrength does not exceed the first signal strength by the amount thewireless device remains connected through the first connection, whereinthe amount may be adjusted at the wireless device by increasing ordecreasing the amount.
 8. The system of claim 7, wherein the amount isadjusted manually using a selector switch onboard the wireless device,the selector switch having multiple states to manually increase ordecrease the amount.
 9. The system of claim 7, further comprising aserving GPRS support node (SGSN) connecting the cellular network to themedia gateway.
 10. The system of claim 7, further comprising an accesspoint connecting the
 802. 1x network to the media server.
 11. The systemof claim 7, further comprising a local exchange carrier (LEC) switchconnecting the media gateway to a plain old telephone service (POTS)network.
 12. The system of claim 11, wherein the terminating station ison the POTS network.
 13. A method of switching a call session, themethod comprising: determining whether a call session is active;retrieving a cellular signal level and a 802.1x signal level from awireless device; and determining whether the cellular signal levelexceeds the 802.1x signal level by an amount, wherein if the cellularsignal level exceeds the 802.1x signal level by the amount the wirelessdevice and the call session switches from a 802.1x connection to acellular connection, and if the cellular signal level does not exceedthe 802.1x signal level by the amount the wireless device remainsconnected in the call session through the 802.1x connection, wherein theamount may be adjusted at the wireless device by increasing ordecreasing the amount.
 14. The method of claim 13, wherein the amount isadjusted using a selector switch on the wireless device, the selectorswitch having multiple states to manually increase or decrease theamount.
 15. The method of claim 13, wherein activation of the selectorswitch increases the amount to prevent a handoff between the 802.1xconnection and the cellular connection.
 16. The method of claim 13,wherein if the cellular signal level exceeds the
 802. 1x signal level bythe amount a call control server signals a media gateway to switch thecall session from the 802.1x connection to the cellular connection.